The present invention relates to centrifuges and, in particular, to the balancing of centrifuges during thawing of frozen materials.
A typical bloodbanking refrigerated centrifuge 2 is shown in FIG. 1 and includes a rotatable rotor 4. Buckets or carriers 6 are pivotally connected to the rotor. This particular centrifuge employs a lid 8 which permits high speed rotation. The carriers swing on axis Axe2x80x94A and assume a horizontal position during centrifuge operation as a result of centrifugal forces caused by spinning of the rotor.
In early centrifuge usage, blood was collected in glass bottles which were placed in cylindrical centrifuge carriers. The bottles were prone to breakage and made decanting liquid a difficult task. This lead to the use of flexible containers or bags in centrifugation. Bags are more convenient in handling and withstand mishaps such as falls much better than glass bottles.
The contents of a centrifuge are to be placed in radial symmetry to the axis of rotation to achieve an approximate balance of masses. The material to be centrifuged is first statically balanced, such as through the use of a two-plate balance, to achieve the same weight in each container. Typically, water is added to increase the weight of a container. Then, the balanced containers are placed in diametrically opposed relationship on the rotor. Therefore, the number of carriers is, for example, four or six rather than an odd number.
Centrifuges evolved into high speed machines. The bags did not always perfectly fit the carriers and ruptured at high pressures. Also, doctors differed in the volume of contents placed in each bag.
Centrifuge adapters were placed in the carriers to simplify operation and avoid bag breakage. Also, adapters were used to place all sorts of small containers, such as xe2x80x9cRadio Immuno Assayxe2x80x9d test tubes in the carriers, to enhance the usefulness of the centrifuge around the laboratory.
Adapters have a rigid construction which is intended to keep the contents safe during the centrifuge run. Some adapters help the centrifuge operator with a difficult part of the separation: taking the centrifuged goods out of the carriers and decanting the supernatant liquid without mixing it with the separated cell packets or pellets. Other adapters prevent whole blood from remaining in the pleats at the top part of the bags, caused when tubing of the bag is placed into the carrier.
Adapters such as those described in U.S. Pat. Nos. 5,549,540 and 4,582,606, employ elliptical cavities defined by rigid walls for separation of liquid/cell combinations. However, such elliptical adapters, as well as cylindrical (circular) adapters, exhibit problems when used on frozen material. Ice clumps that separate from the frozen mass tend to xe2x80x9cfloatxe2x80x9d to sections of the container at lower pressure. The liquid resulting from the melting of the frozen masses flows to high pressure areas replacing their volume. All this happens in an aleatory or haphazard manner in circular and elliptical adapters, whether bags or bottles. Also, the adapters, by virtue of their rigid construction, may rupture bags when ice clumps push against the inner walls of the flexible container supported by the rigid walls. This is a major cause for growing imbalance problems and risk to operator and machine during the run.
The medical community could benefit greatly from safe operation of a centrifuge which prevents flexible bag rupture, especially in the case of thawing frozen contents by centrifuging. Such safe operation should enable centrifuges to be used to thaw biomaterial while avoiding splashing (such as in the case of blood). Other areas that could benefit are blood banks in that they could quickly prepare their own fresh Cryoprecipitated AHF in advance during normal blood bank operation. Summer shortage cases would be solved by the safe use of centrifuges for thawing as would emergency cases by on-the-spot donation by volunteers. Independent operation from commercial blood clotting concentrates for any special reason would be possible. More flexible care of hemophilia, von Willebrand""s disease and other low blood clotting diseases would be possible. Also, new possibilities of investigation may occur as new mixtures of biomedical compounds can be made and studied.
In general, the invention pertains to an adapter for supporting a flexible container or bag in a centrifuge carrier. The adapter is of a size that can be received in a cylindrical cavity of the carrier and comprises a wall formed of a flexible material. The wall comprises a first concave wall portion or section having a first curvature and a second wall portion or section which has a second curvature that is lower than the first curvature. The first wall portion and second wall portion are diametrically opposed to each other so as to receive the flexible container in an interior region substantially bounded by an inner surface of the wall.
In all embodiments of the present invention, it will be appreciated by those skilled in the art that reference to the wall xe2x80x9csubstantially boundingxe2x80x9d the crescent shaped interior region (or interior region between the first concave wall portion having a first curvature and diametrically opposed second wall portion having a lower curvature than the first curvature) includes within its scope walls which do not completely surround the flexible bag that they shape. In a preferred embodiment the interior of the adapter wall completely surrounds the interior region.
More specifically, the invention is directed to an adapter formed of a flexible material. The first and second sections are fastened by a hinge. A latch interconnects the first and second sections together. This two-part adapter may include a plurality of latch openings to adjust the size of the interior region. Flexible containers thus may be contacted with even pressure by the adapter and placed in the resulting shape without room for substantial movement within the interior region of the adapter, regardless of the volume of the flexible container and its contents. In this disclosure, the term xe2x80x9cflexiblexe2x80x9d in regards to the adapter wall, means material which is suitable to withstand freezing of the liquid components of the flexible container and allows flexure of the flexible container during thawing effective to avoid rupture of the flexible container. For example, the adapter should allow a maximum linear dimension distortion of the wall ranging from 0.3 to 1.0 mm when freezing or thawing the bag contents.
In particular, the adapter includes the first concave wall portion and a second convex wall portion having a larger curvature radius (i.e., lower curvature) than the first wall portion, the first and second wall portions being diametrically opposed to each other. The radius of curvature of the first higher curvature, concave wall portion approximates the radius of curvature of the centrifuge carrier, for example, to within a tolerance on the order of 5-10 mm to allow easy setting of the loaded adapter. In this way, the curvature provides a sufficient hold for practical purposes and allows for easy handling of the adapter. Centrifugal force will suffice to retain the adapter in position during centrifugation. The radius of curvature of the low curvature wall portion is, for example, 3 to 4 times the radius of curvature of the high curvature wall portion. As a practical matter it is expected that the adapter will seldom be used alone in a carrier as a second bag can usually be placed in the carrier along with the bag carried by the adapter.
Until now, accelerated thawing of biological material such as plasma or other liquid placed in a flexible container by means of centrifugation, resulted in severe mechanical overload in the centrifuge because of the imbalance created during the run. This put the machine and its operator at risk.
Placing of frozen material in the centrifuge poses no risk as the solid filled soft containers (such as bags) are placed in the carriers and the usual static balancing procedure is followed. This usual practice implies that mass distribution around the axis of rotation is approximately correct, that other changes in mass distribution will not occur or will be negligible during the centrifuge run and that the machine will absorb or compensate for the small imbalance resulting from inevitable displacement from the original position of the contents being centrifuged.
Dynamic balancing of the centrifuge load (i.e., balancing during the run) is difficult for the operator to achieve, as it implies a procedure far more complicated than the static balancing carried out with a standard balance and water (or other media) to equalize the weight of the carriers.
The deformation of the centrifuged material due to the aleatory movement of frozen masses and resulting liquids is a cause of severe dynamic imbalance in the centrifuge and this especially happens in the case of soft containers such as blood donation bags. When solid material contained in the soft container melts down, the resulting liquid flows to a different position than the one it originally had, generating imbalance during the run.
This aleatory movement of frozen masses and liquids is typical of cylindrical and elliptical adapters. Rigid adapters or devices that are used in the separation of liquids and cell packets are unsuitable for thawing biomedical material by centrifugation because they allow for the free movement of frozen masses against the walls of the rigid adapter containing the soft container, and these frozen masses are likely to produce imbalance and breakage of the rigid container. Although the use of flexible adapters has been considered, the flexible container or bag is permitted to assume an elliptical or cylindrical (round) shape, allowing for free movement of frozen masses and liquids during centrifugation with corresponding imbalance.
Although the application of high acceleration during melting of frozen material desirably increases the speed and the amount of material being melted, it aggravates the problem of imbalance detection and machine stoppage. Many centrifuges are equipped with an imbalance detector of some kind. However, in some cases this is unable to solve the problem, as the increase of dynamic imbalance is too quick and may create damage even during the coasting period (from full speed to a complete stop).
One use of the present invention applies to the separation of Cryoprecipitated AHF from whole human blood. It is a usual practice to extract blood from donors and place it in a transfusion bag. The bag is equipped with tubing to decant the separated parts into one or two separate bags, in one or more stages of centrifugation and following additional procedures. To obtain Cryoprecipitated AHF for haemophilic patients, for example, the whole blood is centrifuged to separate the red cell packet, and the resulting platelet-poor plasma is decanted into a second bag. The second bag is separated from the one containing the red cells and sealed. Following the procedure the bag of platelet poor plasma is deeply frozen in a liquid medium at temperatures around or below xe2x88x9270xc2x0 C. This provides for a quick freezing and the separation of the Cryoprecipitated AHF at the solid-liquid interface. Resulting from this procedure is a bag of frozen plasma plus the separated Cryoprecipitated AHF immobilized in the frozen plasma. Until the present invention, this bag was placed in a 4xc2x0 C. or higher temperature deposit and allowed to thaw for about 24 hours. The Cryoprecipitated AHF resulted as a viscous precipitate.
Using the present invention the above procedure is modified whereby the bag of platelet poor plasma is placed in the adapter and conformed into a shape by contact with the adapter wall. This is then deeply frozen in the known manner. When needed, the adapter(s) with frozen contents is placed in a centrifuge and thawed quickly (filling other carriers if needed and statically balancing the centrifuge) in accordance with the present invention, which greatly shortens the time needed to form Factor VII Rich Cryoprecipitate.
The use of moderate acceleration to thaw material such as blood or components thereof typical of bloodbanking centrifuges (e.g., around 2000 to 3000 G""s, wherein G is the acceleration of gravity) reduces the thawing time from 24 hours to about 35 minutes, for example. The safe application of acceleration by centrifuge is made possible by the use of the present invention.
Referring to a general method of the present invention for thawing frozen contents of flexible containers in a centrifuge, the frozen flexible container is contacted with an interior wall of an adapter whereby the container conforms to a crescent shape of an interior region substantially bounded by the wall. The adapter is received in a cylindrical cavity of a carrier. While the flexible container contacts the interior wall of the adapter the rotor is rotated so as to thaw the frozen contents in an ordered manner which maintains the dynamic balance of the centrifuge.
A more specific method of treating biological material contained by a flexible container in a centrifuge in accordance with the invention, comprises placing a flexible container containing liquid biological material in the interior region of an adapter. The adapter wall is pressed into contact with the flexible container so as to shape the flexible container into a crescent shape without space for substantial movement of the flexible container within the adapter. The flexible container and its biological material are frozen in shape. When needed for use, the adapter and the frozen flexible container are then placed in one of the carriers and the centrifuge is statically balanced. The rotor is rotated at a speed (RPM) and for a time sufficient to thaw the frozen contents. The adapter wall is pressed against the frozen flexible container while rotating the rotor, effective to order the thawing of the biological material according to the crescent shape and thereby maintain a dynamic balance of the centrifuge. The biological contents may comprise blood or a component thereof. In a more specific application the biological contents comprise platelet poor plasma in the production and use of Cryoprecipitated AHF.
Many additional features and a fuller understanding of the invention will be had from the accompanying drawings and the detailed description that follows.